1. Field of the Invention
This invention relates to an LED lighting apparatus using an LED (light emitting diode) element as a light source and, in particular, to an LED lighting apparatus that has a high reliability and is downsized as well as having a good heat radiation property corresponding to implementation of a high-output and high-light intensity LED.
2. Description of the Related Art
A lighting apparatus using an LED element as a light source is known. In such a lighting apparatus, light emitted from the LED element can be efficiently directed to a desired radiation direction by providing the LED-mounted substrate or a member disposed around it with a light-reflecting property.
In recent years, a white LED lighting apparatus with a good mass productivity and a long-term reliability is demanded. Especially, it is desired to use the white LED lighting apparatus as a vehicle lighting apparatus such as a headlight. Necessary requirements for the headlight are to have a light-focusing property and light diffusion property enough to direct a white light to a desired radiation range as well as to have a high-light intensity.
It is known to drive a large-size LED element by feeding a large current in order to have a high-intensity white light. However, due to heat generated according to the amount of current fed, emission efficiency of the LED element may be reduced. Furthermore, the light intensity may be reduced by light deterioration of sealing resin such as an epoxy resin and silicone resin to seal the LED element.
To solve these problems, JP Utility-Model Application Laid-Open No. 5-38927 (hereinafter referred to as JP 5-38927) discloses a reflection-type lighting apparatus that a light emitted from an LED element is reflected by a reflector disposed opposed to the LED element, and a lead portion to feed power to the LED element is disposed midway in the traveling direction of light reflected by the reflector without affecting the light extraction property while offering a good heat radiation property.
JP 5-38927 teaches that the lead portion is formed to have a width projected in a direction perpendicular to the traveling direction of the reflected light greater than the width of the LED element and smaller than its width in a direction parallel to the reflected light, and, therefore, the heat radiation property can be improved while suppressing the shading affection of the lead portion constant (See paragraphs [0008] to [0009] and FIG. 1 of JP 5-38927).
However, the lighting apparatus of JP 5-38927 has the following problems.
(1) Since the reflector and the lead portion are integrally sealed with an epoxy resin, the light extraction property may be reduced by the light deterioration of the epoxy resin due to a large amount of heat generated from the LED element caused by an increase in light intensity of the LED element. Thus, the lighting apparatus cannot secure a long-term reliability.
(2) Since heat generated from the LED element is radiated through the lead portion, the lead portion needs to have a radiation area increased according to the heat generation in order to radiate efficiently the increased heat. This causes an increase in apparatus size.